Optical Lattice Clock
magic wavelength · 10⁻¹⁸ accuracy · gravitational redshift
Physics: Optical lattice clock: 10⁴ ⁸⁷Sr atoms trapped in 1D standing wave at magic wavelength λ_magic = 813 nm (AC Stark shift cancels for both clock states). Clock transition ¹S₀ → ³P₀ at 698 nm, linewidth <1 mHz, Q ~ 10¹⁷. Accuracy 10⁻¹⁸ (1 second in 30 billion years). Relativistic redshift: Δf/f = gh/c² ≈ 1.1×10⁻¹⁶/m height. Chou et al. 2010: 33 cm height difference detectable. Chronometric leveling: clock comparisons reveal geoid height differences. Lamb-Dicke confinement eliminates first-order Doppler: recoil energy ≪ phonon energy in trap.